"Of course, Anton, at sixty miles up, the air is so thin that it has hardly any weight. Indeed, we wouldn't know there was any air at that height but for the trail that shooting stars leave. A meteor glows because of friction, and in a vacuum there is no friction. Therefore there must be air at the vast heights where shooting stars are first seen."
"Could an aeroplane get up there?"
The Forecaster shook his head.
"Never," he answered. "Even six miles up, the air would be too thin to sustain the weight of an aeroplane unless the machine were flying at terrific velocity, and besides, at that height, there wouldn't be enough air for an aviator to breathe. At that, Anton, you can see for yourself that if the air is saturated with water vapor—and the cloud-bearing atmosphere is eight or ten miles thick—there is room for a lot of water."
"It's evaporation that puts water into the air, isn't it, sir?" asked Ross.
In the Path of the Lightning.
Courtesy of U.S. Weather Bureau.